1. Field of the Invention
The invention relates to a wireless video camera, and more respectively to cameras and systems of cameras intended to supply live images.
2. Related Art
Professional video cameras serve to film an image sequence so as to replay it generally on a television. Some video cameras are intended to supply live images. The expression “supply live images” should be understood to mean broadcast images to the antenna while the camera is capturing the images. This type of video camera is generally intended for multi-camera professional use.
To be able to supply live images, the most prevalent camera system is a camera linked to a camera control component by way of a triaxial cable better known as a triax. The camera control component allows remote monitoring of most of the parameters of the camera so as in particular to be able to inter-calibrate the cameras during picture shots. The use of a cable yields mobile cameras whose movements are limited by the cable. Operators sometimes have to ensure passage of the cable during displacements of the camera.
It is moreover known to resort to wireless systems in order to circumvent the limitations engendered by the cable. Analog transmission systems are known. A drawback of analog systems is the use of wide bandwidths at high frequencies which necessitate the pointing of the reception antenna. In order to tailor or control the parameters of the cameras, it is known to resort to a return path of much higher frequency and a much narrower spectrum. Should there be an obstacle in the transmission path or should the reception antenna be pointed wrongly, noise appears on the image received by the control component. When the producer reckons that the noise is too great he does not select the camera.
Wireless video cameras using digital transmission are currently offered by camera manufacturers. Various transmission systems are possible. However, all digital transmission systems comprise the use of an error correcting code in order to circumvent the noise-related degradations of the transmission channel. The noise of the channel depends on numerous parameters relating to the environment in which the camera is deployed and relating to the distance between the camera and the antenna of a base station. Worst situation operating conditions are defined so as to have an approximation of the corresponding maximum noise in order to determine which corrector code should be used. Whatever the estimation of the maximum noise of the channel and the corrector code used, there is always a moment at which the camera is in a critical operating situation and when the number of errors to be corrected exceeds the permitted error correction threshold. When the error correction ratio is exceeded, it results in an abrupt loss of image which cannot be anticipated by the producer. Such a problem is especially detrimental to the use of such cameras for supply live images.